Kevin Garnett goes down: Late in the first quarter, Garnett went up for a wide-open dunk, held on to the rim for an extra second as he grimaced in pain and limped up the floor on his left leg. Moments later, Celtics trainer Ed Lacerte worked on the same right leg that kept Garnett from finishing the 2008-09 season and hobbled him last year. Then, the official word: Garnett was out for the remainder of the game with a “lower right leg injury.”

Later, the Celtics stressed it was not a knee or ankle issue, but indeed a lower right leg injury. Garnett underwent X-rays, which showed no fractures, and he’ll have an MRI on Thursday. He walked to the locker and training rooms on his own accord.

Is it New Year’s Day? As Tommy Heinsohn said on the television broadcast, “They’re playing like they’re hungover.” The Celtics looked sluggish, even before the injury to Garnett. In the first quarter alone, they committed eight turnovers and allowed the Pistons to shoot 11-of-20 (55 percent).

In all, the C’s committed 21 turnovers, leading to 23 Pistons points. Detroit also shot 39-of-69 from the field (56 percent) and 10-of-14 from 3-point range (71 percent) for the game. The Celtics even made McGrady appear like the McGrady of old, as he totaled 21 points, eight assists and four rebounds.

Sharing the wealth: In their first matchup of the season, with Rajon Rondo in the starting lineup, the Celtics recorded 20 more assists than the Pistons (33-13) in a 109-86 victory.

This time around? The Pistons actually recorded eight more assists than the C’s (26-18), as Nate Robinson (one assist) got the start in place of the injured Rondo. In fact, the Celtics totaled more turnovers than assists.

WHAT WENT RIGHT

Paul Pierce does it all: With Garnett out for the remainder of the game, all eyes turned to Pierce for leadership on both ends of the floor. He responded — even though his teammates did not. Pierce scored 33 points to go with eight assists, five rebounds and five steals. Allen was the only other Celtic to reach double figures, finishing with 12 points, seven rebounds and four assists.

Jermaine O’Neal contributes: In 23 minutes off the bench, Jermaine O’Neal — who had shown little to nothing since returning on Christmas Day — recorded six rebounds and seven points, making his only two shots from the field. He even drew an important fourth-quarter charge on defense.

While it wasn’t much, O’Neal produced more in this outing than he had in the two previous games combined. If Garnett misses significant time this season, a giant magnifying glass will be focused on O’Neal’s impact.

Free-throw shooting: The Celtics didn’t get to the free-throw line much, but when they did they made them count — making 18-of-19 (94 percent). Pierce, Allen and O’Neal were a combined 14-for-14 from the charity stripe.

In fact, the C’s shot pretty well from everywhere on the floor, making 34-of-66 shots from the field (51 percent) and 6-of-15 3-pointers (40 percent).